Implementing a scalable ospf based solution

www.professordkinney.com
09/01/13
Instructional Design-Computer Networking -
Bridges Educational Group

09/01/13
Implementing a Scalable OSPF-Based Solution

Lessons Summary:
 Implementing OSPF
 Multiarea OSPF IPv4 Implementation
 Troubleshooting Multiarea OSPF
 Examining OSPFv3
09/01/13

OSPF Overview
Creates a neighbor relationship by exchanging hello packets
Propagates LSAs rather than routing table updates
Link: Router interface
State: Description of an interface and its relationship to
neighboring routers
Floods LSAs to all OSPF routers in the area, not just directly
connected routers
Pieces together all the LSAs generated by the OSPF routers
to create the OSPF link-state database
Uses the SPF algorithm to calculate the shortest path to each
destination and places it in the routing table
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OSPF Hierarchy Example
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Minimizes routing table entries
Localizes the impact of a topology change within an area

Neighbor Adjacencies: The Hello Packet
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SPF Algorithm
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Places each router at the root of a tree and calculates the
shortest path to each destination based on the cumulative cost
Cost = Reference Bandwidth / Interface Bandwidth (b/s)

Planning to Deploy OSPF
Prior to deploying an OSPF routing solution, the following
should be considered:
• IP addressing plan
• Network topology
• OSPF areas
Once the requirements have been assessed, the implementation plan can be
created.
Implementing OSPF
The information necessary to implement OSPF routing includes the following:
• The IP addresses to be configured on individual router interfaces.
• A list of routers on which OSPF is to be enabled, along with the OSPF
process number to use and the connected networks that are to run OSPF
and that need to be advertised (per individual router).
• The area in which each interface is to be configured.
• Metrics that need to be applied to specific interfaces, or OSPF traffic
engineering.
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In the implementation plan, OSPF tasks include the following:
• Enabling the OSPF routing protocol, directly on an interface or by using the
correct network command under the OSPF routing process configuration
mode.
• Assigning the correct area id to the interface, via the OSPF configuration on
the interface or under the OSPF routing process configuration mode.
• Optionally configuring the metric to appropriate interfaces.
Verifying OSPF
After implementing OSPF, verification should confirm proper deployment on
each router.
Verification tasks include verifying:
• Verifying that the appropriate OSPF neighbor relationships and
adjacencies are established
• Verifying that the OSPF LSDB is populated with the necessary
information.
• Verifying that IP routing table is populated with the necessary
information.
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• Verifying that there is connectivity in the network between routers and
to other devices.
• Verifying that OSPF behaves as expected in a case of a topology
change, by testing link failure and router failure events.
Documenting
After a successful OSPF deployment, the solution and verification process and
results should be documented for future reference.
Documentation should include:
• A topology map
• The IP addressing plan
• The area hierarchy
• The networks and interfaces included in OSPF on each router
• The default and any special metrics configured
• The verification results.
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Enable OSPF Routing
Define OSPF as the IP routing protocol.
Router(config)#
router ospf process-id
The process-id is an internally used number that identifies the
OSPF routing process.
 The process-id does not need to match process IDs on other routers
 It can be any positive integer in the range from 1 to 65535
Define OSPF networks to advertise to OSPF neighbors.
Router(config-router)#
network ip-address [wildcard-mask] area area-id
The ip-address parameter can be a network, a subnet, or the address of a
directly connected interface.
The wildcard-mask is an inverse mask used to determine how to
interpret the address.
• The mask has wildcard bits, where 0 is a match and 1 is “don’t care.”
• For example, 0.0.255.255 indicates a match in the first 2 octets.
• The area-id parameter specifies the OSPF area to be associated with the
address.
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The Wildcard Mask
Recall that a wildcard mask is the inverse of a subnet mask.
 An easy way to calculate the inverse of the subnet mask, is to subtract the
subnet mask from 255.255.255.255.
 For example, the inverse of subnet mask
255.255.255.252 is 0.0.0.3.
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Optional method to enable OSPF explicitly on an interface.
Router(config-if)#
ip ospf process-id area area-id
The process-id parameter can be a network, a subnet, or the
address of a directly connected interface.
• The area-id parameter specifies the OSPF area to be associated
with the address.
• Because this command is configured explicitly for the interface, it takes
precedence over the network area command.
Define the Interface Bandwidth
Defines the interface’s bandwidth (optional).
Router(config-if)#
bandwidth kilobits
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The kilobits parameter indicates the intended bandwidth in kbps.
 For example, to set the bandwidth to 512,000 bps, use the
bandwidth 512 command.
 The configured bandwidth is used by routing protocols in the metric
calculation.
 The command does not actually change the speed of the interface.
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Configuring Single-Area OSPF
RouterX(config)#
router ospf process-id
Defines OSPF as the IP routing protocol
RouterX(config-router)#
network address wildcard-mask area area-id
Assigns networks to a specific OSPF area
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Configuring Loopback Interfaces
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Router ID:
•Number by which the router is known to OSPF
•Default: The highest IP address on an active interface at the
moment of OSPF process startup
•Can be overridden by a loopback interface: Highest IP
address of any active loopback interface
•Can be set manually using the router-id command

Configuring Multi-Area OSPF
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Alternate Multi-Area OSPF
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OSPF Router ID
A router is known to OSPF by the OSPF router ID number.
• LSDBs use the OSPF router ID to differentiate one router from the
next.
By default, the router ID is the highest IP address on an active interface at the
moment of OSPF process startup.
• However, for stability reason, it is recommended that the router id command or
a loopback interface be configured.
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Define the Router ID
Assign a specific router ID to the router.
Router(config-router)#
router-id ip-address
Any unique arbitrary 32-bit value in an IP address format (dotted
decimal) can be used.
If this command is used on an OSPF process that is already active, then the new
router ID takes effect:
 After the next router reload.
 After a manual restarting of the OSPF process using the clear ip ospf process
privileged EXEC command.
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Verifying the Router-ID
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R2# show ip ospf
Routing Process “ospf 50” with ID 10.64.0.2
<output omitted>

Verifying OSPF
09/01/13

Verifying the OSPF Configuration
RouterX# show ip protocols
Verifies that OSPF is configured
RouterX# show ip route
Displays all the routes learned by the router
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Verifying the OSPF Configuration (Cont.)
RouterX# show ip ospf
Displays the OSPF router ID, timers, and statistics
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show ip protocols
Verify routing protocol information on the router
R1# show ip protocols
Routing Protocol is “ospf 1”
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Router ID 10.64.0.1
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Maximum path: 4
Routing for Networks:
10.0.0.0 0.255.255.255 area 0
Reference bandwidth unit is 100 mbps
<output omitted>
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show ip ospf neighbors
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Verify that the router recognizes OSPF routes
R1# show ip route ospf
10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
O IA 10.2.1.0/24 [110/782] via 10.64.0.2, 00:03:05, FastEthernet0/0
R1#
Clearing the OSPF Routing Table
To clear all routes from the IP routing table, use:
Router# clear ip route *
To clear a specific route from the IP routing table, use:
Router# clear ip route A.B.C.D
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show ip ospf interface
Verify OSPF configured interfaces.
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OSPF Network Types
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Broadcast
DR /BDR election required since there could be many devices.
• Establishing adjacencies with all routers in a broadcast network would
easily
overload a router due to the overhead of maintaining those adjacencies.
• Instead, OSPF routers form full adjacencies with the DR and BDR only.
Packets to all OSPF routers are forwarded to 224.0.0.5.
Packets to the DR / BDR are forwarded to 224.0.0.6.
09/01/13

Broadcast Challenge: Multiple Adjacencies
A challenge of broadcast network is the number of adjacencies that
would be required.
• One adjacency for every pair of routers.
• This would increase network traffic and load on each router to
manage each individual adjacency.
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Designated Router
A designated router (DR) and backup designated router (BDR) solve
these challenges because they:
• Reduce routing update traffic
• Manage link-state synchronization
The DR is elected and becomes responsible for maintaining the topology
table for the segment.
This DR has two main functions:
• To become adjacent to all other routers on the network segment.
• To act as a spokesperson for the network.
As spokesperson the DR becomes the focal point for collecting and
sending routing information (LSAs).
09/01/13

Backup Designated Router (BDR)
For fault tolerance, a second router is elected as the BDR.
• The BDR must also become adjacent to all routers on the network
and must serve as a second focal point for LSAs.
• However, the BDR is not responsible for updating the other routers or
sending network LSAs.
The BDR keeps a timer on the DR's update activity to ensure that it is
operational.
• If the BDR does not detect activity from the DR after the timer expires,
the BDR immediately becomes the DR and a new BDR is elected.
09/01/13

DR/BDR
DRs and BDRs are elected on a per-network basis and
therefore each network segment has its own DR and BDR.
• For example, a router connected to multiple multiaccess broadcast
networks can be a DR on one segment and a regular (DROTHER)
router on another segment.
The election process is accomplished dynamically using the
Hello protocol.
• However, the election can be manually manipulated the ip ospf
priority number interface configuration command.
After a DR and BDR have been selected, any router added to the
broadcast network establishes full adjacencies with the DR and BDR
only.
09/01/13

Assigning Router Priority
Assign a specific OSPF priority to the router.
Router(config-if)#
ip ospf priority number
A router interface can have a priority number between 0 - 255:
0 = DROTHER - Router cannot be a DR
1 = Favorable - Default for all routers
255 = Very favorable - Ensures at least of a tie.
The priority must be configured before the election takes place to figure
into the election.
To display an interface's priority value and other key information use the
show ip ospf interface command.
09/01/13

The Election of the DR
All neighbors with a priority > 0 are listed.
2. The router with highest priority is elected DR.
If there is a tie, the highest router IDs are used.
3. If there is no DR, the BDR is promoted as DR.
4. The neighbor with the next highest priority is elected BDR
Manipulating the Election Process
The DR / BDR maintain these roles until they fail even when more
routers with higher priorities show up on the network.
To influence the election of DR & BDR, do one of the following:
• Boot up the DR first, followed by the BDR, and then boot all other
routers.
OR
• Shut down the interface on all routers, followed by a no shutdown
on the DR, then the BDR, and then all other routers.
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Point-to-Point
Both routers become fully adjacent to each another.
Usually a serial interface running either PPP or HDLC.
• May also be a point-to-point subinterface running Frame Relay or ATM.
No DR /BDR election required since there are only two devices.
OSPF autodetects this type of network.
Packets are sent to 224.0.0.5
09/01/13

OSPF over MPLS
Multi-Protocol Label Switching (MPLS) is an Internet Engineering Task
Force (IETF) standard architecture that combines the advantages of
Layer 3 routing with the benefits of Layer 2 switching.
A unique feature of MPLS is its capability to perform label stacking, in
which multiple labels can be carried in a packet.
The top label, which is the last one in, is always processed
first.
• Label stacking enables multiple LSPs to be aggregated, thereby
creating tunnels through multiple levels of an MPLS network.
09/01/13

OSPF over Layer 3 MPLS VPN
The customer and provider edge routers are running OSPF.
• However the internal provider routers do not.
The customer has to agree upon OSPF parameters with the service
provider (SP) to ensure connectivity.
• These parameters are often governed by the SP.
09/01/13

OSPF over Layer 2 MPLS VPN
The Layer 2 MPLS VPN backbone and the provider routers
are not visible to the customer routers.
• A neighbor relationship is established directly between OSPF enabled
routers over the MPLS backbone, and behaves in the same way as
on an Ethernet broadcast network therefore DR and BDR routers are
elected
09/01/13

Nonbroadcast Multiaccess (NBMA)
Frame Relay, ATM, and X.25 are examples of NBMA networks.
The default OSPF hello and dead intervals on NBMA interfaces are 30
seconds and 120 seconds, respectively.
Although NBMA networks can support more than two routers, they have
no inherent broadcast capability.
• This can create reachability issues.
To implement broadcasting or multicasting, the router
replicates the packets to be broadcast or multicast and
sends them individually on each permanent virtual circuit
(PVC) to all destinations.
• This process is CPU and bandwidth intensive.
09/01/13

DR Election in an NBMA Topology
By default, OSPF cannot automatically build adjacencies with neighbor
routers over NBMA interfaces.
OSPF considers the NBMA environment to function similarly to other
multiaccess media such as Ethernet.
• However, NBMA networks are usually hub-and-spoke (star) topologies
using PVCs or switched virtual circuits (SVCs).
• In these cases, the physical topology does not provide the multiaccess
capability on which OSPF relies.
The election of the DR becomes an issue in NBMA topologies because
the DR and BDR need to have full Layer 2 connectivity with all routers
in the NBMA network.
The DR and BDR also need to have a list of all the other routers so that
they can establish adjacencies
09/01/13

OSPF over NBMA Topology
There are five NBMA topology modes of operation:
• Two official OSPF modes described in RFCs
• Three customized Cisco modes.
RFC 2328-compliant modes are as follows:
• Nonbroadcast (NBMA)
• Point-to-multipoint
Cisco modes are as follows:
• Point-to-multipoint nonbroadcast
• Broadcast
• Point-to-point
OSPF NBMA topology modes are configured using the ip ospf network
interface configuration command.
• Some modes require that a neighbor be manually configured using the
neighbor router configuration command.
09/01/13

Subinterfaces
OSPF can also be run over subinterfaces.
• A subinterface is a physical interface that can be split into multiple
logical interfaces.
• Each subinterface requires an IP subnet.
Subinterfaces can be defined as either a point-to-point or multipoint
interface.
• A point-to-point subinterface has similar properties to a physical
pointto-point interface.
Note:The ip ospf network command is not required.
Define a Subinterface
Router(config)#
interface serial number.subinterface-number {multipoint
| point-to-point}
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Using Point-to-point Subinterfaces
Characteristics:
• Same properties as any physical point-to-point physical interface
• DR and BDR not required.
• One IP subnet per subinterface pair.
• Used when only 2 routers need to form an adjacency on a pair of
interfaces.}
09/01/13

Using Multipoint Subinterfaces
The example has one point-to-point subinterface and one multipoint
subinterface.
• The multipoint subinterface supports two other routers in a single
Multipoint Frame Relay
subinterfaces default to OSPF nonbroadcast mode, which requires
neighbors to be statically configured and a DR and BDR election.
09/01/13

Troubleshooting Multiarea OSPF
Verifying OSPF Operability
An essential requirement of your network operation is that the status of
your routers and routing protocols is monitored to ensure network
availability for all users.
The 3 basic forms of network monitoring include router SYSLOG files,
SNMP and MIBs, and using show commands.
One useful configuration practice is to configure your routers to use DNS
names in all OSPF show command displays.
This feature makes it easier to identify a router because the router is
displayed by name rather than by its router ID or neighbor ID.
ip ospf name-lookup is used to configure OSPF to display IP addresses by
their DNS names instead.
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One very useful troubleshooting tool is keeping track of events that affect a router's
operation with logging.
SYSLOG on a router with a SYSLOG server is the recommended practice, since without a
server, you are limited to the memory on the router for record keeping.
The storage of the logs on a SYSLOG server is useful for trend analysis, forensic gathering,
and troubleshooting viewpoint.
This can also help you find system error messages, outages, and a variety of other network
events that may have already passed and been lost in a router's memory.
You first need to decide the level of logging that you wish to use, with 8 possible options to
choose from.
The logging levels are as follows:
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show logging is used to display the addresses and levels associated with the current
logging setup as well as any other logging statistics.
You also want to ensure that the SYSLOG entries are stamped with the correct time and
date.
service timestamp log datetime localtime show-timezone is used to configure the router to
automatically data and time stamp all SYSLOG entries on the router and when sent to
the SYSLOG server.
show ip ospf border-routers displays the internal OSPF routing table to an ABR or ASBR.
09/01/13

show ip ospf database displays the contents of the topology database
maintained by the router.There is actually a list of various forms of this command that can
be used to deliver information about different OSPF link-state advertisements.
show ip ospf database asbr-summary displays a large variety of
information in the OSPF database for an ASBR.
show ip ospf database database-summary is used to provide
a summary of every type of LSA that has been sent, deleted, or expired because of Maxage.
show ip ospf database external provides information regarding the
OSPF database external LSAs.
show ip ospf database network provides information regarding the
OSPF database network LSAs, which includes where the routes came from in the network
and which routers are part of the network by OSPF area.
show ip ospf database router provides information regarding the OSPF
database router LSAs
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show ip ospf neighbor [interface-name | detail] is used
to display OSPF neighbor information on a per-interface basis.
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show ip ospf neighbor ip-address is used to provide detailed
information regarding a specific OSPF network as specified by the IP address.
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clear ip ospf process [process-id] is used to completely reset either
a specific OSPF process, or all OSPF processes on a router.
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The Debugging OSPF Command:
Among information provided by this command is the :
i. Debug ip ospf packet: this command displays hello packets being sent and received on
your router
ii. Debug ip ospf hello: this command displays hello packets being sent and received on
your router. It also displays more information than the debug ospf packet
iii. The debug ip ospf adj: shows DR and DBR elections on a broadcast and non-broadcast
multi-access (NBMA) network.
debug ip ospf hello displays information about how OSPF Hellos are operating within the
OSPF domain.
debug ip ospf packet displays a LOT of detailed information about each OSPF packet
received.
Be aware that this produces a set of information for EACH packet received.
09/01/13

Examining OSPFv3
OSPFv3 / OSPFv2 Similarities
Basic packet types
Hello, DBD, LSR, LSU, LSA
• Mechanisms for neighbor discovery andadjacency formation
• Interface types
P2P, P2MP, Broadcast, NBMA, Virtual
• LSA flooding and aging
• Nearly identical LSA types
V2, V3 Differences
OSPFv3 Is Running per Link Instead of per IP Subnet
• A link by definition is a medium over which two nodes can communicate at link layer
• In IPv6 multiple IP subnet can be assigned to a link and two nodes in different subnet can
communicate at link layer therefore OSPFv3 is running per link instead of per IP subnet
• An Interface connect to a link and multiple interface can be connected to a link
09/01/13

Support of Multiple Instance per Link
New field (instance) in OSPF packet header allow running multiple instance per link
• Instance ID should match before packet being accepted
• Useful for traffic separation, multiple areas per link and AF
Address Semantic Change in LSA
Router and Network LSA carry only topology information
• Router LSA can be split across multiple LSAs; Link State ID in LSA header is a fragment ID
• Intra area prefix are carried in a new LSA payload called intra-area-prefix-LSAs
• Prefix are carried in payload of inter-area and external LSA
Generalization of Flooding Scope
• In OSPFv3 there are three flooding scope for LSAs (link-local scope, area scope, AS scope)
and they are coded in LS type explicitly
• In OSPFv2 initially only area and AS wide flooding was defined; later opaque LSAs
introduced link local scope as well
Explicit Handling of Unknown LSA
The handling of unknown LSA is coded via U-bit in LS type
• When U bit is set, the LSA is flooded with the corresponding flooding scope, as if it was
understood
• When U bit is clear, the LSA is flooded with link local scope
• In v2 unknown LSA were discarded
09/01/13

Authentication Is Removed from OSPF
Authentication in OSPFv3 has been removed and OSPFv3 relies now on IPv6 authentication
header since OSPFv3 run over IPv6
• Autype and Authentication field in the OSPF packet header therefore have been
suppressed.
OSPF Packet format has been changed
• The mask field has been removed from Hello packet
• IPv6 prefix are only present in payload of Link State update packet
Configuring OSPFv3 in Cisco IOS® Software
Similar to OSPFv2
Prefixing existing Interface and Exec mode commands with “ipv6”
• Interfaces configured directly Replaces network command
• “Native” IPv6 router mode Not a sub-mode of router ospf
09/01/13

Configuration modes in OSPFv3
• Entering router mode
[no] ipv6 router ospf <process ID>
• Entering interface mode
[no] ipv6 ospf <process ID> area <area ID>
• Exec mode
show ipv6 ospf [<process ID>]
clear ipv6 ospf [<process ID>]
Cisco IOS OSPFv3 Specific Attributes
Configuring area range
[no] area <area ID> range <prefix>/<prefix length>
• Showing new LSA
show ipv6 ospf [<process ID>] database link
show ipv6 ospf [<process ID>] database prefix
• Configuring authentication
Under ipv6 router ospf: area 0 authentication ipsec spi 256 md5 cisco
Under interface:
ipv6 ospf authentication ipsec spi 256 md5 cisco
09/01/13
09/01/13

OSPFv3 Debug Commands
Adjacency is not appearing
[no] debug ipv6 ospf adj
[no] debug ipv6 ospf hello
• SPF is running constantly
[no] debug ipv6 ospf spf
[no] debug ipv6 ospf flooding
[no] debug ipv6 ospf events
[no] debug ipv6 ospf lsa-generation
[no] debug ipv6 ospf database-timer
• General purpose
[no] debug ipv6 ospf packets
[no] debug ipv6 ospf retransmission
[no] debug ipv6 ospf tree
09/01/13

OSPFv3 Configuration Example
09/01/13

Enhanced Routing Protocol Support Cisco IOS OSPFv3
Router2#sh ipv6 ospf int pos 3/0
POS3/0 is up, line protocol is up
Link Local Address FE80::290:86FF:FE5D:A000, Interface ID 7
Area 1, Process ID 100, Instance ID 0, Router ID 10.1.1.4
Network Type POINT_TO_POINT, Cost: 1
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Index 1/1/1, flood queue length 0
Next 0x0(0)/0x0(0)/0x0(0)
Last flood scan length is 3, maximum is 3
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 10.1.1.3
Suppress hello for 0 neighbor(s)
09/01/13

Enhanced Routing Protocol Support Cisco IOS OSPFv3
Router2#sh ipv6 ospf neighbor detail
Neighbor 10.1.1.3
In the area 1 via interface POS3/0
Neighbor: interface-id 8, link-local address FE80::2D0:FFFF:FE60:DFFF
Neighbor priority is 1, State is FULL, 12 state changes
Options is 0x630C34B9
Dead timer due in 00:00:33
Neighbor is up for 00:49:32
Index 1/1/1, retransmission queue length 0, number of retransmission 1
First 0x0(0)/0x0(0)/0x0(0) Next 0x0(0)/0x0(0)/0x0(0)
Last retransmission scan length is 2, maximum is 2
Last retransmission scan time is 0 msec, maximum is 0 msec
09/01/13

Router2#sh ipv6 route
IPv6 Routing Table - 5 entries
Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP
U - Per-user Static route
I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea
O - OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
OI 2001:db8:FFFF:1::/64 [110/2]
via FE80::2D0:FFFF:FE60:DFFF, POS3/0
C 2001:db8:1:1::/64 [0/0]
via ::, POS3/0
L 2001:db8:1:1::1/128 [0/0]
via ::, POS3/0
L FE80::/10 [0/0]
via ::, Null0
L FF00::/8 [0/0]
via ::, Null0
09/01/13

Cisco IOS OSPFv3 Database Display
09/01/13

OSPFv3 on IPv6 Tunnels over IPv4
09/01/13

Lessons Learned:
What is OSPF and its configuration
Troubleshooting OSPF
OSFV3 what it is and its configuration.
09/01/13

Implementing a scalable ospf based solution

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